I know I'm just a teenager, but my co-workers who may be not even 2 years older than me all thought I was like 12 when I first came into work. Because I look ages younger than them they don't take me seriously, and talk to me like I'm incompetent and it really gets on my nerves.
thats just the way the world is sorry to say. people don't like to listen to instruction especially from their junior, even though your probably in the right. unless your already in a position of power of some sort. I say embrace your youth, when your old you'll think damn I want to look young again. just persevere would be the best, show them all you'll put up with any amount of crap and shake it off like it never happened.
I can understand how annoying that must be, but looking older isn't always better. Enjoy your youthful look. And if you're wanting to use like makeup to look older, then that's okay, but it probably won't do you justice.
In time that will stop. I had the same the problem with my job. But over time they start to look at you just like anyone else.